By measuring how energy waves move through the sky above Earth, scientists have created a way to delve into the 13.8 billion-year history of our universe, starting from “first light.”
The team, led by Johns Hopkins University astrophysicists, used an array of microwave telescopes called the Cosmology Large Angular Scale Surveyor (CLASS) to map 75% of the sky on Earth. This observatory is located in the Andes mountain range, approximately 5,860 meters above Chile’s Atacama Desert.
Measurements made by CLASS relate to “microwave polarization”, which is related to the direction in which light waves align. These measurements will help scientists filter the wavelength of radiation emitted from the Milky Way due to the early light of the universe, the so-called “cosmic microwave background,” or CMB.
“By studying the polarization of the CMB, astrophysicists can infer what the universe must have been like in earlier times,” Tobias Marriage, co-leader of the team and Johns Hopkins professor of physics and astronomy, said in a statement. said. “Astrophysicists can go back to very, very old times, to the initial conditions, to the earliest moments when the distribution of matter and energy in the universe first emerged, and they can relate all of that to what we see today.”
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Decoding the cosmic fossil
The CMB consists of light left over from an event that occurred about 380 million years after the Big Bang, during a period called the “epoch of recombination.” Until this point, the universe was filled with a hot, dense plasma that made it opaque. These so-called cosmic dark ages were caused by free electrons endlessly bouncing around particles of light called photons.
Then, the era of recombination began when the universe expanded and cooled enough to allow electrons to bond with protons, forming the first atoms and giving rise to Hydrogen, the lightest and simplest element in the universe. The sudden absence of free electrons meant that photons could instantly travel freely and the universe became transparent to light.
This first light is seen today as CMB.
Because it dates back to times when the universe was much denser than it is today, CMB is almost evenly spread throughout the cosmos. However, there are small variations in the CMB, and since this radiation has existed for approximately 13.4 billion years, it is these variations that tell the story of matter and how its distribution evolved. This includes the formation of the first stars, galaxies, and galactic clusters.
“Studying residual radiation from the beginning of the universe is critical to understanding how the entire universe formed and why it is the way it is,” said Nigel Sharp, program director in the Division of Astronomical Sciences at the National Science Foundation. The statement stated that CLASS has been used for more than ten years. “These new measurements provide important large-scale detail within our growing picture of the variations present in cosmic background radiation, a particularly impressive achievement because it was achieved using ground-based instruments.”
CLASS maps provide information about a microwave signal called linear polarization, which is emitted when light is confined to a single plane. The linear polarization of microwaves is the result of the Milky Way’s magnetic field knocking electrons around at high speeds. This signal could help study the Milky Way, but it could also hinder the study of the early universe using the CMB.
By clearly mapping the microwave sky and allowing scientists to filter out linearly polarized microwaves, CLASS can improve our understanding of the physical processes present in the early universe. These processes would have the capacity to create a background of circular polarization. Circular polarization occurs when light behaves like a two-dimensional transverse wave; It differs from linear polarization microwaves.
“Knowing the brightness of the emission from our Milky Way galaxy is very important because we need to correct for it to do a deeper analysis of the cosmic microwave background,” said Joseph Eimer, an astrophysicist at Johns Hopkins University and lead author of the study. he said in the statement. “CLASS is very good at characterizing the nature of this signal so we can recognize it and remove these contaminants from the observations.”
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With the presentation of these new results, CLASS has set a new standard for mapping the polarization of light, breaking new ground for an Earth-based observatory that may need to combat interference from our planet’s atmosphere.
“The project is at the forefront of pushing ground-based polarization measurements at the largest scales,” Elmer said.
The team’s research was published Feb. 26 in The Astrophysical Journal.